Low temperature co-fired ceramic (LTCC) structures are well-known and provide a potential for high density, high reliability, high performance and low cost interconnect packages. The LTCC structure is comprised of low loss, co-fireable glass-ceramic dielectric tape and compatible co-fireable thick film conductive compositions that are typically screen printed directly onto the individual green sheet layers. Embedded devices such as resistors, capacitors and inductors may be applied to the individual green sheets. Vias are formed in each layer and filled to provide electrical connections between the individual layers and the layers and the outer surfaces of the LTCC. The individual layers are laminated and then fired to produce a LTCC. Thick film conductive compositions can be screen printed onto the outer surfaces of the co-fired LTCC and then fired. Multilayer LTCC processing, including thick film compositions printing on Green tapes, lamination methods and high temperature firing processes are further described in U.S. Pat. No. 7,687,417 and U.S. Pat. No. 7,611,645.
A representative cross-section of a LTCC structure with thick film conductive compositions screen printed onto the outer surfaces is shown in FIG. 1. The LTCC structure 10 contains glass-ceramic dielectric layers 11 and screen printed thick film inner conductors 12. Thick film via interconnects 13 provide electrical connections between the inner conductors 12 and thick film via interconnects 14 provide electrical connections between the inner conductors 12 and the thick film outer conductor 15 on the upper surface 16 of the LTCC and the thick film outer conductor 17 on the lower surface 18 of the LTCC.
The screen printed thick film outer conductors have the disadvantage of limited spatial resolution.
There is a need for outer conductors with narrow conductor line widths and dose spacing between conductor lines for use in microwave and millimeter wave frequency applications.